Outline• Introduction to Structural Engineering
• Design Process
• Forces in Structures
• Structural Systems
• Materials
• Definitions of Important Structural Properties
• Triangles
• UNITS (Dimensional Analysis)
Structural Engineering
• What does a Structural Engineer do?
– A Structural Engineer designs the structural systems and structural elements in buildings, bridges, stadiums, tunnels, and other civil engineering works (bones)
– Design: process of determining location, material, and size of structural elements to resist forces acting in a structure
Design Process
Engineering Design Process
• Identify the problem (challenge)• Explore alternative solutions
– Research past experience
– Brainstorm
– Preliminary design of most promising solutions
• Analyze and design one or more viable solutions• Testing and evaluation of solution
– Experimental testing (prototype) or field tests
– Peer evaluation
• Build solution using available resources (materials, equipment, labor, cost)
Design Process in Structural Engineering
• Select material for construction
• Determine appropriate structural system for a particular case. Justify (tell me why) you used these particular structural systems.
• Determine forces acting on a structure
• Calculate size of members and connections to avoid failure (collapse) or excessive deformation
Forces in Structures
Forces Acting in Structures
• Force induced by gravity (F=ma)
– Dead Loads (permanent): self-weight of structure and attachments
– Mass Vs. Weight
– Compression, Tension, bending, torsion
Forces Acting in Structures
Vertical: Gravity Lateral: Wind, Earthquake
Forces in Structural Elements100
lb
Compression
100 lb
Tension
Forces in Structural Elements 100
lb
Bending
Torsion
Structural Systems
Typical Structural Systems
Arch
Typical Structural Systems
TrussC
T
CCT
Forces in Truss Members
Typical Structural Systems
Frame
Typical Structural Systems
Flat Plate
Typical Structural Systems
Folded Plate
Typical Structural Systems
Shells
Providing Stability for Lateral Loads
Racking Failure of Pinned Frame
Braced Frame Infilled Frame Rigid Joints
Materials Used in Civil Engineering
Metals– Cast Iron– Steel– Aluminum
• Concrete
• Wood
• Fiber-Reinforced Plastics
Engineering Properties of Materials
• Steel– Maximum stress: 40,000 – 120,000 lb/in2
– Maximum strain: 0.2 – 0.4– Modulus of elasticity: 29,000,000 lb/in2
• Concrete– Maximum stress: 4,000 – 12,000 lb/in2
– Maximum strain: 0.004– Modulus of elasticity: 3,600,000 – 6,200,000 lb/in2
• WoodValues depend on wood grade. Below are some samples– Tension stress: 1300 lb/in2
– Compression stress: 1500 lb/in2
– Modulus of elasticity: 1,600,000 lb/in2
Concrete Components
• Sand (Fine Aggregate)
• Gravel (Coarse Aggregate)
• Cement (Binder)
• Water
• Air
Fiber-Reinforced Composites
PolymerMatrix
Polyester
Epoxy
Vinylester
Fiber Materials
Glass
Aramid (Kevlar)
CarbonFunction of fibers:
•Provide stiffness•Tensile strength
Functions of matrix:
•Force transfer to fibers•Compressive strength•Chemical protection
Composite
Laminate
Properties of Materials
(Why are they used)
Definition of Stress
Section X
T
T
Section X
Stress = Force/Area
T
Example (English Units):
T = 1,000 lb (1 kip)A = 10 in2.
Stress = 1,000/10 = 100 lb/in2
Example (SI Units):
1 lb = 4.448 N (Newton)1 in = 25.4 mm
T = 1,000 lb x 4.448 N/lb = 4448 NA = 10 in2 x (25.4 mm)2 = 6450 mm2
(1 in)2
Stress = 4448/6450 = 0.69 N/mm2
(MPa)
Definition of Strain
L
T
T
Lo
Strain = L / Lo
Example:
Lo = 10 in.L = 0.12 in.
Strain = 0.12 / 10 = 0.012 in./in.
Strain is dimensionless!!(same in English or SI units)
Engineering Properties of Structural Elements
• Strength– Ability to withstand a given stress without failure
• Depends on type of material and type of force (tension or compression)
Tensile Failure Compressive Failure
Engineering Properties of Structural Elements
• Stiffness (Rigidity)
– Property related to deformation
– Stiffer structural elements deform less under the same applied load
– Stiffness depends on type of material (E), structural shape, and structural configuration
– Two main types
• Axial stiffness
• Bending stiffness
Axial Stiffness
L
T
T
Lo
Stiffness = T / L
Example:
T = 100 lbL = 0.12 in.
Stiffness = 100 lb / 0.12 in. = 833 lb/in.
Bending Stiffness
Stiffness = Force / Displacement
Example:
Force = 1,000 lbDisplacement = 0.5 in.
Stiffness = 1,000 lb / 0.5 in. = 2,000 lb/in.
Displacement
Force
Stiffness of Different Structural Shapes
Stiffest
StifferStiff
Types of Structural Elements – Bars and Cables
Bars can carry either tensionor compression Cables can only carry tension
Types of Structural Elements – Beams
Tension
Compression
Loads
Triangles
Formulas
• SOH, CAH, TOA
• c2 = a2 + b2
H
A
O